Hyperthyroidism Flashcards

1
Q

Give a brief overview of how T3 and T4 synthesis works

A

TSH travels from anterior pituitary In blood to follicular cells in the thyroid

This allows for the uptake of iodide

Iodide undergoes iodination your form iodine

Thrroglobulin is released into the colloid

Thyroid peroxidase enzyme is also released which is important for iodination

Iodine and thyroglobulin undergo iodination to form MIT and DIT

These undergo coupling reactions to form T3 and T4

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is the hypothalmo-pituitary-thyroid axis and what is the result?

A

TRH (thyrotrophin releasing hormone) from hypothalamus ->

TSH (thyroid stimulating hormone) from anterior pituitary ->

T3 and T4 from thyroid

T3 and 4 have an inhibitory effect on both TRH and TSH

The role of T4 (which is deiodinated to the active form T3) and T3 is to increase basal metabolic rate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

How is primary hypothyroidism treated?

A

Primary means thyroid is damaged so can’t make T4

Give levothyroxine

Adjust dose (increase) until TSH levels go down to normal range (in primary hypothyroidism TSH will be high)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is graves disease?

A

Causes hyperthyroidism

Autoimmune

Anti TSH-receptor antibodies bind to TSH receptors in the thyroid which causes excess T4 to be made

Causes a smooth goitre

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What are the symptoms of Graves’ disease?

A

Perspiration

Exophthalmos

Pre tibial myxoedema

Tremor

Goitre

Weight loss

Increased appetite

Tachycardia

Palpitations

Diarrhoea

Heat intolerance

All are due to increased basal metabolic rate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

How does Graves’ disease cause exophthalmos?

A

Graves is auto immune

Other antibodies bind to muscles behind the eye, causing the muscles to grow, pushing the eye out

This can threaten visionary

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is Pretibial myxoedema and what causes it in graves?

A

Swelling of the lower extremities (before the tibia). Doesn’t involve fluid (unlike pitting oedema which occurs in heart failure), it is an increase in soft tissue

It is caused by a different antibody that those that cause high T4 and exophthalmos

(Don’t confuse it with myxoedema that is advanced hypothyroidism)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What does a radioiodine scan look like in Graves’ disease?

A

Diffuse enlargement and engorgement of thyroid gland, also symmetrical

The whole gland is overactive so takes up the radioiodine equally so you can see the whole shape of the gland, it will also be enlarged.

The pyramidal lobe often lights up too

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What does a radioiodine scan look like with a hyper functioning adenoma?

A

Adenoma will be a large lump on one side of the gland usually. The goitre will be asymmetric.

The rest of the gland shrinks

It isn’t as active so doesn’t take up as much iodine and doesn’t appear as bright as the thyroid in Graves

The lump will show up the most as this takes up more iodine

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What are the effects of iodithyronines on the sympathetic nervous system?

A

Sensitises beta 2 adrinergic receptors to ambient levels of adrenaline and noradrenaline

:. There is apparent sympathetic activation

Leads to:
Tachycardia
Palpitations
Hand tremor
Lid lag (eyelids held open)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What are the symptoms of hyperthyroidism (too much thyroxine) ?

A

Weight loss despite increased appetite

Breathlessness

Tachycardia

Palpitations

Sweating

Heat intolerance (hot in winter)

Diarrhoea

Lid lag (and other sympathetic features)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is a thyroid storm?

A

Happens when people, for whatever reason don’t want to go to hospital

It has a 50% mortality if untreated

Blood results confirm hyperthyroidism

Needs aggressive treatment

Symptoms:
Hyperpyrexia >41°c
Accelerated tachycardia (>170) /arrhythmia 
Cardiac failure
Delirium/frank psychosis
Hepaticellar dysfunction; jaundice 

Must have 2 or more of these symptoms

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

How is hyperthyroidism treated?

A

Three options:

Surgery (thyroidectomy)

Radioiodine

Drugs

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What are the types of drugs used in hyperthyroidism treatment?

A
  1. Thionamides (anti thyroid drugs):
    Propylthiouracil (PTU)
    Carbimazole(CBZ)
    Used as daily treatment for Graves and toxic thyroid nodule
  2. Potassium iodide:
    Large loads of iodine can completely stop the thyroid gland working for a while
  3. Radioiodine:
    Can kill the gland
  4. Beta blockers:
    These are given along with thionamides as they stop sympathetic activity so help with some of the symptoms
    Propanolol used as it is non specific (unlike bisoprolol which only treats heart sympathetic symptoms)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is the mechanism of action of thionamides? And how long are they prescribed?

A

They inhibit the action of thyroid peroxidase enzymes (help with iodination). This stops T4 synthesis

The biochemical effect takes hours

But the clinical effect takes weeks. This is because there are stores of leftover thyroxine which have to be used up

Therefore it is often given alongside propanolol (beta blocker) which rapidly reduces tremor and tachycardia

Usually aim to stop anti thyroid drug treatment after 18 months

Patient is then reviewed periodically to test for relapse/remission

Only half of patients are cured

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What are some side effects of thionamides?

A

Agranulocytosis (reduction in neutrophils) - rare and reversible on withdrawal of drug

Rashes - more common

17
Q

Why are beta blockers given along with thionamides?

A

Takes several weeks for thionamides to have an effect

So beta blockers are given in the mean time to reduce symptoms caused by increased sympathetic activity (tachycardia, tremor)

A non selective beta blocker is used
Eg. Propanolol

As selective ones eg. Bisoprolol would only treat the heart sympathetic symptoms

18
Q

When is potassium iodide used? And what is it’s mechanism of action?

A

Given in doses at least 30x average daily requirement

Used to prepeare patients for surgery

And in severe thyrotoxic crisis (thyroid storm)

Causes inhibition of thyroid hormone synthesis and secretion. By the Wolff-Chaikoff effect

Inhibits iodination of thyroglobulin, and inhibits Peroxide generation and thyroperoxidases

Reduced hyperthyroid symptoms in 1-2 days

Vascularity and size of glad reduce in 10-14 days

Can’t use long term as eventually the thyroid ends up actually using all of that iodine

19
Q

What are the risks of thyroid surgery?

A

Risk of voice change due to proximity to the recurrent laryngeal nerve

Also risk to parathyroid glands - role in calcium regulation, it increases calcium levels

You’ll get a scar

And anaesthetic risks

20
Q

How does radioiodine therapy work?

A

Swallow capsule containing 370 MBq of the isotope I-131

It is contradicted in pregnancy as radioactivity will harm the baby

The person will be radioactive so will need to avoid children and pregnant people for a few days

Iodine is expensive, so for scans 99-Tc Pertechnetate is used

21
Q

What is viral thyroiditis and it’s symptoms?

A

Hyperthyroidism caused by a viral infection

Aka de quervains thyroiditis

Hyper at first, as stores are released, then hypo later as virus is replicating so thyroid isn’t making hormones 
Symptoms:
Painful dysphagia
Hyperthyroiditis
Pyrexia 
Thyroid inflammation (usually more on one side)
Pain
Tender paratracheal lymph nodes
22
Q

What is the history/process of viral thyroiditis?

A

Virus attacks the thyroid gland causing pain and tenderness

Thyroid stops making thyroxine and makes virus instead

Therefore there is no iodine uptake at all

During the first 4 months stored T4 is released

After this stores run out so you become hypothyroid for a month

Then resolution occurs

Do not treat it, you’ll just mess up the timeline

After 3 months there is a slow recovery

(Post partum thyroiditis is similar but there is no pain and you have a baby). Caused because pregnancy modulates the immune system

23
Q

What does a viral thyroiditis radioiodine scan look like?

A

Nothing at all

Coz there is Zero iodine uptake as the thyroid is busy making virus